The present invention pertains to automatic headlamp control using a wave transceiver.
It has long been desired to provide an automatic headlamp system which is capable of automatically switching between low and high beam headlamps when oncoming and preceding vehicles are detected. Several systems have been developed to fulfill this need. For example, numerous systems utilize an optical sensor, such as a silicon photodiode, to sense the light from the headlamps of an oncoming vehicle. Although commercialized many years ago, these systems are not currently commercially available due to difficulties sensing vehicle tail lamps and an inability to distinguish between lamps on other vehicles and non-vehicular light sources such as street lights and houses.
More recently systems have been developed that employ an electronic imaging system to detect lights from oncoming and preceding vehicles. Such systems perform far more satisfactorily than non-imaging light sensor systems due to their ability to make intelligent decisions about the relevance of different light sources. In general, the relevance of a light source to head light brightness control is determined using information about a light source""s brightness, position, and color. A system of this type is disclosed in U.S. Pat. No. 5,837,994, entitled CONTROL SYSTEM TO AUTOMATICALLY DIM VEHICLE HEAD LAMPS, issued to Joseph Scott Stam et al. on Nov. 17, 1998, the disclosure of which is incorporated herein by reference. This system determines the presence of other vehicles based upon the luminance projected onto an imaging system from the lamps of the other vehicles.
Although imaging systems provide significantly better performance than non-imaging systems, efforts continue toward the development of further improvements in automatic headlight control systems for a number of reasons. In order to avoid dazzling an oncoming driver, an automatic high beam dimming system should switch to low beams by the time an oncoming vehicle is within about 700 feet of the controlled vehicle. In order to handle the wide brightness variations in commercial headlamps found on different vehicles, the system must be set up to transition from high to low beams when the illumination projected onto the controlled vehicle""s imaging system from an oncoming vehicle""s headlamp reaches a threshold corresponding to the lowest output headlamp that is commercially available being within 700 feet of the control vehicle. However, if the oncoming vehicle has a high output headlamp, the projected illumination will reach that threshold when the oncoming vehicle is significantly farther than 700 feet away. As a result, the headlamps will transition from high to low beams prematurely in the presence of a vehicle having higher output headlamps. Although this behavior is not distracting to drivers, it does not allow for maximum utilization of the high beam headlamps. An additional complication occurs when the oncoming or preceding vehicle is traveling at an angle to the control vehicle, as occurs on curves, rather than exactly in parallel with the control vehicle. Headlamp and tail lamp brightness is greatest directly in front of the lamps, and decreases rapidly as the off-center angle (the angle relative to a line projecting straight out directly in front of the lamp) increases. This characteristic of vehicle headlamps and tail lamps greatly reduces the ability of a light responsive system to accurately detect the presence of another vehicle when the other vehicle is not traveling parallel with the controlled vehicle. Additionally, vehicle taillights can be particularly difficult to detect due to the wide variation in brightness of taillights on different vehicles and their susceptibility to diminished brightness due to environmental conditions, such as rain, fog and the presence of salt or dirt on the lamp lens.
In addition to its other capabilities, the system disclosed in U.S. Pat. No. 5,837,994 can make an estimate of the distance to another vehicle. This estimate is made by assuming that light sources have a common brightness and then estimating the distance to a light source as being proportional to the inverse of the square root of the projected luminance. To accurately measure the distance, it is necessary to know the actual brightness of the light source. Due to the wide variations in brightness of headlamps and tail lamps commercially offered on vehicles, and other issues described hereinabove, it is only possible to approximate the distance of another vehicle using this method.
Another technique for measuring the distance of a vehicle is disclosed in Japanese Laid-open patent application No. Heisei 6-312056, published Jun. 25, 1996. This application discloses an image sensor used to capture an image of on oncoming vehicle and determines the distance to the vehicle based on the spacing of the two headlamps of the vehicle in the image. A very high resolution image sensor is necessary to properly resolve the two headlamps as distinct objects in the image. In addition to the expensive high-resolution image sensor, such a system would require high quality optics as well as a sophisticated processing system to process the large amount of image data in a reasonable time. Therefore such a system is currently too expensive to be commercially viable. Furthermore, even after processing the light information through such a costly system, the accuracy is low. The low accuracy is due to a number of variables including the problem that the spacing of the headlamps on the vehicle is necessarily estimated since this spacing varies on different vehicles and it is not known whether the other vehicle is traveling in parallel with the subject vehicle.
Advanced headlamp systems transition from high beam to low beam gradually to maximize the available road illumination to the driver of the control vehicle without negatively impacting other drivers. These systems may additionally vary the vertical aim of headlamps or steer the beams horizontally. Such headlamp systems and their control are described in U.S. Pat. No. 5,837,994 entitled CONTROL SYSTEM TO AUTOMATICALLY DIM VEHICLE HEAD LAMPS, issued to Jon Bechtel et al. on Nov. 17, 1998; U.S. Pat. No. 6,049,171, entitled CONTINUOUSLY VARIABLE HEADLAMP CONTROL, filed on Sep. 18, 1998, by Joseph Scott Stam et al.; and U.S. patent application Ser. No. 09/528,389, entitled IMPROVED VEHICLE LAMP CONTROL, filed by Joseph Stam on the same date as this application, the disclosures of all of which are incorporated herein by reference thereto. These more sophisticated headlamp systems would further benefit from knowing the actual distance, speed and location of oncoming or preceding vehicles.
Accordingly, it is desirable to provide a more effective system for controlling the headlights of a vehicle.